Apparatus and method for controlling a terminal accessing a base station in broadband wireless communication system

ABSTRACT

A circuit includes a controller to determine whether to prohibit entry of an end unit to a base station in a wireless communication network, the controller configured to process a media access control (MAC) management message that includes a timer value, the timer value designating a time period during which entry is prohibited.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 15/974,361, filed on May 8, 2018, which is a continuationapplication of prior application Ser. No. 12/326,376, filed on Dec. 2,2008, which has issued as U.S. Pat. No. 9,986,488 on May 29, 2018 andwas based on and claimed priority under 35 U.S.C § 119(a) of a Koreanpatent application number 10-2007-0128178, filed on Dec. 11, 2007, inthe Korean Intellectual Property Office, the disclosure of which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a broadband wireless communicationsystem, and in particular, to an apparatus and a method for controllinga terminal accessing a base station in a broadband wirelesscommunication system.

Description of the Related Art

In a 4^(th) generation (4G) communication system, research for providingservices having various Quality of Service (QoS) using transmissionspeeds of about 100 Mbps is in active progress. Particularly, researchfor supporting high speed services in the form of guaranteeing mobilityand QoS for a broadband wireless access (WBA) communication system, suchas short-distance wireless communication network system and wirelessmetropolitan area network (WMAN) system, is in active progress. As anexample, communication systems complying with the Institute ofElectrical and Electronics Engineers (IEEE) 802.16 specification isrepresentative of such a system.

The IEEE 802.16 system standard defines various procedures, such as theoperation of a Media Access Control (MAC) layer. Examples of MAC layerprocedures include an initial ranging procedure and a handoverprocedure. Described below are procedures for initial ranging andhandover initiated by a terminal in accordance with the IEEE 802.16system standard.

The initial ranging procedure according to the IEEE 802.16 systemstandard is performed as follows. To initiate initial ranging, aterminal transmits one of a plurality of prescribed ranging codes to abase station. In response thereto, the base station transmits a responsemessage RaNGing ReSPonse (RNG_RSP) message to the terminal. The RNG_RSPmessage includes ranging status TypeLengthValue (TLV). If the basestation is in a status that does not allow ranging of the terminal(i.e., the entry of the terminal to the base station), the base stationsets the ranging status TLV to “abort” to inform the terminal of aranging-not-allowed status. Accordingly, the terminal detects when itsrequest for entry is not allowed and then scans other base stations forentry.

The handover procedure according to the IEEE 802.16 system standard isperformed as follows. To initiate handover, a terminal scans neighboringbase stations and transmits information of scanned neighboring basestations MOBile_Mobile Station HandOver-REQuest (MOB_MSHO-REQ) messagethat includes information of target base station candidates to itsserving base station. Accordingly, the serving base station confirmswhether the target base station candidates included in the MOB_MSHO-REQmessage received from the terminal can support service for the terminal.At this point, the serving base station transmits a MOBile_Base StationHandOver-ReSPonse (MOB_BSHO-RSP) message indicating that a target basestation has been found to the terminal. The MOB_BSHO-RSP messageincludes information of the target base station candidates that canprovide the requested handover. The terminal that has received theMOB_BSHO-RSP message selects a target base station and transmits aMOBile_HandOver-INDication (MOB_HO-IND) message to inform the servingbase station of the selected target base station. The serving basestation that has confirmed the target base station selected by theterminal provides information regarding the terminal to the target basestation, and the terminal performs an entry procedure to connect to thetarget base station.

As described above, the base station can limit entry of the terminalduring the initial ranging procedure. However, the base station cannotprevent the terminal from immediately trying to access the base stationagain, that is, retrying the initial ranging procedure. When theterminal immediately re-requests the base station for entry, there is ahigh possibility that the entry request will be denied again since thestatus of the base station has not yet changed. Therefore, immediatelyrequesting entry again by the terminal causes waste of wirelessresources. In addition, a terminal that has performed handover to changethe serving base station may initiate handover again to the previousserving base station. Repeatedly performing handover between two basestations also causes waste of wireless resources, and repeatedlyattempting handover itself wastes wireless resources. Therefore, thereis a need to prevent unnecessary attempts for entry as well as actualexecution of entry procedures.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an apparatus and amethod to prevent unnecessary attempts for entry and access of a networkin a broadband wireless communication system.

Another object of the present invention is to provide an apparatus and amethod to prohibit a terminal from attempting re-entry to a specificbase station in a broadband wireless communication system.

Still another object of the present invention is to provide an apparatusand a method for informing an entry prohibition time of a specificterminal with respect to a specific base station in a broadband wirelesscommunication system.

According to an aspect of the present invention, a base stationapparatus in a broadband wireless communication system includes acontroller to determine whether to prohibit an entry attempt of aterminal, a generator to generate a media access control (MAC)management message including a value of a timer, the value representingprohibition of entry attempt, and a transmitter to transmit the MACmanagement message to the terminal.

According to another aspect of the present invention, a terminalapparatus in a broadband wireless communication system includes areceiver to receive a media access control (MAC) management message froma base station, a reader to confirm existence of a value of a timerincluded in the MAC management message, the value representingprohibition of entry attempt, and a controller to designate the basestation as prohibited for entry attempt until expiration of the timer.

According to still another aspect of the present invention, a method foroperating a base station in a broadband wireless communication systemincludes determining whether to prohibit an entry attempt of a terminal,generating a media access control (MAC) management message including avalue of a timer, the value representing prohibition of entry attempt,and transmitting the MAC management message to the terminal.

According to yet another aspect of the present invention, a method foroperating a terminal in a broadband wireless communication systemincludes receiving a media access control (MAC) management message froma base station, confirming existence of a value of a timer included inthe MAC management message, the value representing prohibition of entryattempt, and designating the base station as being prohibited from entryattempt until expiration of the timer.

According to yet another aspect of the present invention, a circuitincludes a controller to determine whether to prohibit entry of an endunit to a base station in a wireless communication network, thecontroller configured to process a media access control (MAC) managementmessage that includes a timer value, the timer value designating a timeperiod during which entry is prohibited.

According to yet another aspect of the present invention, a methodincludes determining whether to prohibit entry of an end unit to a basestation in a wireless communication network and processing a mediaaccess control (MAC) management message that includes a timer value, thetimer value designating a time period during which entry is prohibited.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a view illustrating an example of signal exchange during aninitial ranging procedure in a broadband wireless communication systemaccording to the present invention;

FIG. 2 is a view illustrating an example of signal exchange during ahandover procedure in a broadband wireless communication systemaccording to the present invention;

FIG. 3 is a block diagram illustrating a base station in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 4 is a block diagram illustrating a terminal in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention;

FIG. 5 is a view illustrating the operating procedure of a base stationin a broadband wireless communication system according to an exemplaryembodiment of the present invention; and

FIG. 6 is a view illustrating the operating procedure of a terminal in abroadband wireless communication system according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described herein below withreference to the accompanying drawings.

Exemplary embodiments of the present invention provide a system andmethod to prevent unnecessary attempts for entry and access to a basestation by a terminal in a broadband wireless communication system. Forpurposes of example, the exemplary embodiments of the present inventionare illustrated in conjunction with a wireless communication systemusing an orthogonal frequency division multiple access (OFDMA) scheme.However, it is to be understood that the present invention may beimplemented on wireless communication systems using other schemeswithout departing from the scope of the present invention.

To limit attempts of entry by a terminal, the present invention definesa TypeLengthValue (TLV) for exchanging entry limit timer information asillustrated in Table 1. The TLV defined by the present invention may beincluded in various MAC management messages, such as RaNGing-ReSPonse(RNG-RSP) messages, Base Station HandOver-REQuest (BSHO-REQ) messages,and Base Station HandOver-ReSPonse (BSHO-RSP) messages. However, it isto be understood that the entry limit timer TLV of the present inventionmay be included in other messages without departing from the scope ofthe present invention.

TABLE 1 Type Length Value Scope Xx 1 0-255: In units of 100 RNG-RSPmilliseconds BSHO-REQ BSHO-RSP

As illustrated in Table 1, a TLV for limiting entry of a terminalaccording to the present invention represents a timer value. In anexemplary embodiment, the length of the TLV is 1 byte, and the valuethereof expresses entry limit time in units of 100 milliseconds. Whenthe value is 0, it means that an entry limit time is infinite. However,it is to be understood that other data lengths and units of timerepresented by its value may be used without departing from the scope ofthe present invention. For convenience in explanation, the presentinvention calls the TLV on Table 1 an “entry limit timer TLV.”

FIG. 1 illustrates an example of signal exchange during an initialranging procedure between a terminal and a base station in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention.

As shown in FIG. 1, a terminal 110 transmits a ranging request message(e.g., RNG-REQ) to a base station 120 in order to enter a network (step101). The base station 120 that has received the ranging request message(e.g., RNG-REQ) recognizes that the terminal 110 desires to access thebase station 120 and determines whether to allow entry of the terminal110. Based on the result of the determination step, the base station 120may decide that entry to the base station 120 cannot be allowed (step103). For example, the base station 120 may determine that the entry ofthe terminal 110 cannot be allowed due to reasons such as resourceshortage, service unavailable, etc.

In such a situation, the base station 120 transmits a ranging responsemessage (e.g., RNG-RSP) that includes an entry limit timer TLV to theterminal 110 (step 105). That is, the base station 120 transmits theranging response message (e.g., RNG-RSP) including ranging status TLV(e.g., ranging status TLV set to “abort”) to inform the terminal of thedenial of entry to the base station 120 and an entry limit timer TLV toinform the terminal of the prohibition of entry to the base station 120for a predetermined time. Here, the entry limit timer TLV includes timeinformation prohibiting the entry. At this point, the base station mayalso incorporate downlink frequency override TLV into the rangingresponse message (e.g., RNG_RSP). The downlink frequency override TLVincludes frequency allocation (FA) information recommended to a terminaldesigned to induce the terminal to make an entry request through adifferent frequency.

The terminal 110 that has received the ranging response message (e.g.,RNG-RSP) including the ranging status TLV and the entry limit timer TLVrecognizes that an entry request by the terminal 110 has been rejected,and simultaneously, confirms the entry limit timer TLV to recognize thatattempts of entry to the base station 120 is prohibited for thepredetermined time (step 107).

Accordingly, the terminal 110 does not try entry to the base station 120for the predetermined time but rather scans other accessible basestations (step 109). Further, if the ranging response message (e.g.,RNG-RSP) includes the downlink frequency override TLV, the terminal 110scans for accessible base stations at the different FA designated by thedownlink frequency override TLV. If, on the other hand, the rangingresponse message (e.g., RNG-RSP) does not include the downlink frequencyoverride TLV, the terminal 110 scans for accessible base stations at thesame FA.

After the scanning step 109, the terminal 110 performs a network entryprocedure again. At this point, even though the base station 120 isdetermined to be the most appropriate base station to connect to, i.e.,has the best channel status, the terminal 110 does not try entry to thebase station 120 while the predetermined time confirmed in step 107 hasnot expired.

FIG. 2 illustrates an example of signal exchange during a handoverprocedure between a terminal and a base station in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention.

As shown in FIG. 2, a terminal 210 transmits a handover request message(e.g., MOB_MSHO-REQ) to a serving base station 220 in order to switch (ie, handover) to an adjacent base station (step 201). Here, the handoverrequest message (e.g., MOB_MSHO-REQ) may include information of a targetbase station 230.

The serving base station 220 that has received the handover requestmessage (e.g., MOB_MSHO-REQ) transmits a handover pre-notificationmessage (e.g., HO_pre_notification) to the target base station 230 (step203). The handover pre-notification message (e.g., HO_pre_notification)is a message for confirming whether the entry of the terminal 210 can beaccepted. The target base station 230 that has received the handoverpre-notification message (e.g., HO_pre_notification) determines whetherthe entry of the terminal 210 may be accepted and transmits a handoverpre-notification response message (e.g., HO_pre_notification-RSP)informing the acceptance/denial of the handover request to the servingbase station 220 (step 205).

If the handover request has been accepted by the target base station230, the serving base station 220 that has received the handoverpre-notification response message (e.g., HO_pre_notification-RSP)transmits a base station handover response message (e.g., MOB_BSHO-RSP)including an entry limit timer TLV to the terminal 210 (step 207). Thatis, the serving base station 220 transmits the base station handoverresponse message (e.g., MOB_BSHO-RSP) to the terminal that includesinformation of the target base station 230 that has accepted the entryrequest of the terminal 210 and an entry limit timer TLV to inform theterminal of prohibition of entry to the serving base station 220 for apredetermined time.

The terminal 210 that has received the base station handover responsemessage (e.g., MOB_BSHO-RSP) recognizes the target base station 230 thathas accepted the entry request of the terminal 210 and simultaneouslyconfirms the entry limit timer TLV to recognize that entry to theserving base station 220 is prohibited for the predetermined time (step209). Thereafter, once the terminal 210 decides to initiate handover tothe target base station 230, the terminal 210 transmits a handoverindication message (e.g., MOB_HO-IND) to inform the serving base station220 that handover to the target base station 230 is to be performed(step 211).

The serving base station 220 that has received the handover indicationmessage (e.g., MOB_HO-IND) provides information of the terminal 210 tothe target base station 230 (step 213). For example, the information ofthe terminal 210 may include information of service in use and abilityinformation of the terminal 210. Once the target base station 230receives the information of the terminal 210, the terminal 210 and thetarget base station 230 exchange access procedure messages and initiatesaccess (step 215).

Once the process illustrated in FIG. 2 have been completed, the terminal210 does not try entry to the serving base station 220 if thepredetermined time confirmed in step 209 has not expired, even if theserving base station 220 has been considered for handover. In otherwords, when the predetermined time has not lapsed, the terminal 210suspends handover to the serving base station 220. Though only onetarget base station is illustrated as a target base station candidate inFIG. 2 for convenience, a plurality of target base station candidatesmay exist.

FIG. 3 illustrates a block diagram of a base station in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention.

As shown in FIG. 3, the base station includes an RF receiver 302, anOFDM demodulator 304, a subcarrier demapper 306, a symbol demodulator308, a decoder 310, a ranging code detector 312, a message reader 314,an MAC controller 316, a message generator 318, an encoder 320, a symbolmodulator 322, a subcarrier mapper 324, an OFDM modulator 326, and an RFtransmitter 328.

The RF receiver 302 down-converts a radio frequency (RF) signal receivedthrough an antenna into a baseband signal. The OFDM demodulator 304classifies a signal provided by the RF receiver 302 on an OFDM symbolbasis, removes a cyclic prefix (CP), and restores complex symbols mappedto a frequency domain through a fast Fourier transform (FFT) operation.The subcarrier demapper 306 extracts complex symbols mapped to thefrequency domain on a process basis. For example, the subcarrierdemapper 306 extracts signals mapped to a ranging subcarrier andprovides the extracted signals to the ranging code detector 312. Thesymbol demodulator 308 demodulates complex symbols and converts thedemodulated complex signals into a bit stream. The decoder 310channel-decodes the bit stream to restore an information bit stream.

The ranging code detector 312 detects a ranging code transmitted by aterminal. That is, the ranging code detector 312 detects which rangingcode has been transmitted by performing a correlation operation onsignals mapped to a ranging subcarrier and ranging codes prescribed inadvance.

The message reader 314 reads an MAC management message received from aterminal. For example, the message reader 314 reads a ranging requestmessage (e.g., RNG-REQ) from a terminal for entry into a network toconfirm the terminal intending to enter the network. Also, the messagereader 314 confirms target base station candidates by reading a handoverrequest message (e.g., MOB_MSHO-REQ) from a terminal and confirms atarget base station to which information of the terminal should beprovided by reading a handover indication message (e.g., MOB_HO-IND)that includes information of the target base station determined by theterminal.

The MAC controller 316 controls overall functions of the MAC layer ofthe base station. For example, when a terminal tries initial ranging,the MAC controller 316 determines whether to allow entry of the terminalon the basis of available wireless resources and available services, forexample. Also, when a terminal requests handover, the MAC controller 316confirms with a target base station as to whether the handover of theterminal is acceptable.

Particularly, in accordance with the present invention, the MACcontroller 316 determines whether to prohibit entry attempts by theterminal. In this case, entry (i.e., access to a base station) may be byinitial ranging or handover. For example, in the case where a terminalis denied entry to the base station through initial ranging, the MACcontroller 316 prohibits the denied terminal from trying entry (i.e.,initial ranging) to the base station for a predetermined time. In thecase where a terminal performs handover to an adjacent base station, theMAC controller 316 prohibits the terminal performing the handover fromtrying entry (i.e., handover) to the base station for a predeterminedtime.

The message generator 318 generates an MAC management message to betransmitted to a terminal. For example, the message generator 318generates a ranging response message (e.g., RNG-RSP), which is aresponse to an entry attempt by the terminal, a base station handoverresponse message (e.g., MOB_BSHO-RSP), which is a response to a handoverrequest from the terminal, and a base station handover request message(e.g., MOB-BSHO-REQ) to request the terminal to perform a handover.Particularly, in accordance with the present invention, the messagegenerator 318 generates a parameter representing prohibition of entryattempts to the base station for a predetermine time, such as an MACmanagement message including an entry limit timer TLV. For example, theentry limit timer TLV may be included in the ranging response message(e.g., RNG-RSP), the base station handover response message (e.g.,MOB_BSHO-RSP), or the base station handover request message (e.g.,MOB_BSHO-REQ) depending on entry attempt. The entry limit timer TLV maybe configured as shown in Table 1.

When the MAC management message, the ranging response message (e.g.,RNG-RSP), for example, the ranging response message (e.g., RNG-RSP) mayinclude at least one of a parameter representing denial of entry (e.g.,ranging status TLV), a parameter representing prohibited time period forentry (e.g., entry limit timer TLV), and a parameter indicating adifferent frequency (FA) (e.g., downlink frequency override TLV) throughwhich an entry is recommended. When the MAC management message is thebase station handover response message (e.g., MOB_BSHO-RSP) or the basestation handover request message (e.g., MOB_BSHO-REQ), the base stationhandover response/request message (e.g., MOB_BSHO-RSP or MOB_BSHO-REQ)may include at least one of a parameter representing prohibited timeperiod for entry (e.g., entry limit timer TLV) and a parameteridentifying target base station candidate(s) that can accept a handover.

The encoder 320 channel-codes an information bit stream. The symbolmodulator 322 modulates the channel-coded bit stream and converts themodulated bit stream into complex symbols. The subcarrier mapper 324maps the complex symbols to a frequency domain. The OFDM modulator 326converts the complex symbols mapped to the frequency domain into signalsin a time domain through the inverse fast Fourier transform (IFFT)operation and inserts a CP to form an OFDM symbol. The RF transmitter328 up-converts a baseband signal into an RF signal and transmits the RFsignal through the antenna.

FIG. 4 illustrates a block diagram of a terminal in a broadband wirelesscommunication system according to an exemplary embodiment of the presentinvention.

As shown in FIG. 4, the terminal includes an RF receiver 402, an OFDMdemodulator 404, a subcarrier demapper 406, a symbol demodulator 408, adecoder 410, a signal strength measuring unit 412, a message reader 414,an MAC controller 416, a message generator 418, an encoder 420, a symbolmodulator 422, a subcarrier mapper 424, an OFDM modulator 426, and an RFtransmitter 428.

The RF receiver 402 down-converts an RF signal received through anantenna into a baseband signal. The OFDM demodulator 404 classifies asignal provided from the RF receiver 402 on an OFDM symbol basis,removes a CP, and restores complex symbols mapped to a frequency domainthrough the FFT operation. The subcarrier demapper 406 extracts complexsymbols mapped to the frequency domain on a process basis. For example,while the terminal scans a base station for network entry or handover,the subcarrier demapper 406 extracts a signal for scanning, e.g., apreamble signal, and provides the preamble signal to the signal strengthmeasuring unit 412. The symbol demodulator 408 demodulates complexsymbols and converts the demodulated complex symbols into a bit stream.The decoder 410 restores an information bit stream by channel-decodingthe bit stream.

The signal strength measuring unit 412 measures strength of a signalreceived from a base station. For example, the received signal strengthcan be expressed by received signal strength indication (RSSI),signal-to-noise ratio (SNR), signal-to-interface-and-noise ratio (SINR),carrier-to-interference-and-noise ratio (CINR), etc.

The message reader 414 reads an MAC management message received from abase station. For example, the message reader 414 confirms whetherinitial ranging is allowed by reading a ranging response message (e.g.,RNG-RSP), which is a response to an initial ranging request, confirms atarget base station that can accept a handover by reading a base stationhandover response message (e.g., MOB_BSHO-RSP), which is a response to ahandover request, and confirms an acceptable target base station withrespect to a handover by reading a base station handover request message(e.g., MOB-BSHO-REQ) to request the terminal to perform a handover.Particularly, in accordance with the present invention, the messagereader 414 confirms a parameter representing prohibition of entryattempts to a base station for a predetermined time, that is, the entrylimit timer TLV. In this case, entry (i.e., access to a base station)may be by initial ranging or handover. For example, the entry limittimer TLV may be included in the ranging response message (e.g.,RNG-RSP), the base station handover response message (e.g.,MOB_BSHO-RSP), or the base station handover request message (e.g.,MOB_BSHO-REQ) depending on the entry attempt. The entry limit timer TLVmay be configured as shown in Table 1.

The MAC controller 416 controls overall functions of the MAC layer ofthe terminal. For example, when the terminal tries initial ranging, theMAC controller 416 controls the terminal to generate and transmit aranging request message (e.g., RNG-REQ). Also, when the terminalrequests a handover, the MAC controller 416 controls the terminal togenerate and transmit a handover request message (e.g., MOB_MSHO-REQ)including information of collected target base station candidates. TheMAC controller 416 controls the terminal depending on allowance/denialstatus included in a ranging response message (e.g., RNG-RSP), which isa response to an initial ranging attempt. For example, in the case wherean entry to a base station through initial ranging is rejected, the MACcontroller 416 controls the terminal to scan for other base stations toenter the network. In the case of handover, the MAC controller 416controls the operation of the terminal depending on information oftarget base station candidates that can accept a handover included in abase station handover response message (e.g., MOB_BSHO-RSP), which is aresponse to a handover request from the terminal That is, the MACcontroller 416 controls the terminal to select one of the target basestation candidates that can accept a handover and transmit a handoverindication message (e.g., MOB_HO-IND) to inform the selected target basestation.

Particularly, in accordance with the present invention, when an entrylimit timer TLV is detected in a received MAC management message, theMAC controller 416 prohibits entry attempts to the base station that hastransmitted the MAC management message for a predetermined timedesignated by the entry limit timer TLV, that is, until the timer hasexpired. For example, in the case where the entry limit timer TLV isincluded in the ranging response message (e.g., RNG-RSP), the MACcontroller 416 prohibits entry attempts to the base station that hastransmitted the ranging response message (e.g., RNG-RSP) for apredetermined time. That is, when the base station that has transmittedthe ranging response message is selected again as a result of scanningfor base stations in order to enter a network, the MAC controller 416controls the terminal to try initial ranging to one of the base stationsother than the base station that has transmitted the ranging responsemessage if the predetermined time has not expired. When the entry limittimer TLV is included in the base station handover response message(e.g., MOB_BSHO-RSP) or the base station handover request message (e.g.,MOB_BSHO-REQ), the MAC controller 416 prohibits entry attempts, i.e.,attempts for handover, to the base station that has transmitted the basestation handover response/request message (e.g., MOB_BSHO-RSP orMOS_BSHO-REQ) for a predetermined time.

The message generator 418 generates an MAC management messagetransmitted to a base station. For example, the message generator 418generates a handover request message (e.g., MOB_MSHO-REQ) to request ahandover, a handover indication message (e.g., MOB_HO-IND) that includesinformation of a selected target base station for handover, and aranging request message (e.g., RNG-REQ) to initiate initial ranging.

The encoder 420 channel-codes an information bit stream. The symbolmodulator 422 modulates the channel-coded bit stream and converts themodulated bit stream into complex symbols. The subcarrier mapper 424maps the complex symbols to a frequency domain. The OFDM modulator 426converts the complex symbols mapped to the frequency domain into signalsin a time domain through the IFFT operation, and inserts a CP to form anOFDM symbol. The RF transmitter 428 up-converts a baseband signal intoan RF signal, and transmits the RF signal through the antenna.

FIG. 5 illustrates the operating procedure of a base station in abroadband wireless communication system according to an exemplaryembodiment of the present invention.

As shown to FIG. 5, in step 501, the base station confirms whether aterminal performs handover to an adjacent base station, or whether aninitial network entry of the terminal is rejected. Specifically, whenthe terminal performs the handover, the base station confirms whether atleast one of target base station candidates can accept the handover ofthe terminal. Alternatively, when an entry request of the terminalthrough initial ranging occurs, the base station confirms whether entryis rejected because of resource shortage or service unavailable.

In step 503, once the terminal performs handover to an adjacent basestation or the initial network entry of the terminal is rejected, thebase station determines to prohibit the terminal from trying entry tothe base station for a predetermined time. Here, entry (i.e., access tothe base station) may be by initial ranging or handover. It is to beunderstood that the length of time for prohibition (i.e., thepredetermined time) may vary depending on the specific instance withoutdeparting from the scope of the present invention.

In step 505, once it has been determined to prohibit the terminal fromtrying entry, the base station generates a parameter representingprohibition of entry attempts, that is, an MAC management messageincluding an entry limit timer TLV. For example, the entry limit timerTLV may be included in the ranging response message (e.g., RNG-RSP), thebase station handover response message (e.g., MOB_BSHO-RSP), or the basestation handover request message (e.g., MOB_BSHO-REQ) depending on theattempted entry. The entry limit timer TLV may be configured as shown inTable 1.

When the MAC management message is the ranging response message (e.g.,RNG-RSP), the ranging response message may include at least one of aparameter representing denial of entry (e.g., ranging status TLV), aparameter representing prohibited time period for entry (e.g., an entrylimit timer TLV), and a parameter indicating a different frequency (FA)(e.g., downlink frequency override TLV) through which an entry isrecommended. When the MAC management message is the base stationhandover response message (e.g., MOB_BSHO-RSP) or the base stationhandover request message (e.g., MOB_BSHO-REQ), the base stationresponse/request message (e.g., MOB_BSHO-RSP or MOB_BSHO-REQ) mayinclude at least one of a parameter representing prohibited time periodfor entry (e.g., entry limit timer TLV) and a parameter identifyingtarget base station candidate(s) that can accept a handover.

In step 507, the base station transmits the MAC management messagegenerated in step 505 to the appropriate terminal.

FIG. 6 illustrates the operating procedure of a terminal in a broadbandwireless communication system according to an exemplary embodiment ofthe present invention.

As shown to FIG. 6, in step 601, the terminal confirms whether an MACmanagement message is received from a base station.

In step 603, when the MAC management message is received, the terminalconfirms whether a parameter representing prohibition of entry attempts(i.e., an entry limit timer TLV) is included in the MAC managementmessage by reading the MAC management message. Here, entry (i.e., accessto a base station) may be by initial ranging or handover. For example,the entry limit timer TLV may be included in a ranging response message(e.g., RNG-RSP), a base station handover response message (e.g.,MOB_BSHO-RSP), or a base station handover request message (e.g.,MOB_BSHO-REQ) depending on the attempted entry. The entry limit timerTLV may be configured as shown in Table 1. That is, the terminalconfirms the existence of entry limit timer TLV by reading the rangingresponse message (e.g., RNG-RSP), the base station handover responsemessage (e.g., MOB_BSHO-RSP), and the base station handover requestmessage (e.g., MOB_BSHO-REQ). If the entry limit timer TLV is notdetected in the MAC management message, the terminal performs step 607(described below).

When the entry limit timer TLV is detected, in step 605, the terminalsets prohibition of entry attempts to the base station that hastransmitted the MAC management message for a predetermined time, thatis, until expiration of a timer. Accordingly, the terminal does not tryentry to the base station when the predetermined time has not expiredeven if the base station is selected as an optimum base station afterscanning for network entry or for handover.

Subsequently, in step 607, the terminal performs MAC layer operationaccording to the received MAC management message. For example, when theMAC management message is a ranging response message (e.g., RNG-RSP) andranging status TLV is set to “abort,” the terminal scans for basestations to enter the network. Alternatively, when the MAC managementmessage is a base station handover response/request message (e.g.,MOB_BSHO-RSP or MOB_BSHO-REQ), the terminal selects a target basestation to which handover is to be made and transmits information of theselected target base station to a serving base station.

Accordingly, unnecessary entry attempts and unnecessary execution ofentry procedures by a terminal in a broadband wireless communicationsystem are prevented due to prohibition of re-entry attempts using aparameter representing a time period prohibiting entry attempts wheninitial ranging is rejected or handover of the terminal.

Although the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. Therefore, the scope of the presentinvention should not be limited to the above-described embodiments butshould be determined by not only the appended claims but also theequivalents thereof

What is claimed is:
 1. A base station in a wireless communicationsystem, the base station comprising: a transceiver; and at least oneprocessor coupled to the transceiver and configured to: receive, from aterminal via the transceiver, a first signal for a random access,transmit, to the terminal via the transceiver, a message including avalue indicating a length of time in response to receiving of the firstsignal, and receive, from the terminal via the transceiver, a secondsignal for the random access after a time that is determined based onthe value indicating the length of time, wherein the first signal isselected based on a code among a plurality of predefined codes.
 2. Thebase station of claim 1, wherein the value indicating the length of timeindicates one value identified from a plurality of candidate values, andwherein the plurality of the candidate values has a uniform distributionbetween a maximum value and a minimum value.
 3. The base station ofclaim 1, wherein the time is determined based on a predeterminedrelationship between the value indicating the length of time and one ofa plurality of time periods, wherein the plurality of time periodsincludes zero (0) millisecond (ms), and wherein the value indicating thelength of time indicates one value identified from a plurality ofcandidate values including
 0. 4. The base station of claim 1, whereinthe value indicating the length of time indicates a time period duringwhich access of the base station by the terminal is prohibited.
 5. Thebase station of claim 4, wherein the message including the valueindicating the length of time further includes: an indicator forrejecting access to the base station, and an indicator for recommendinga different frequency through which the terminal is to access the basestation.
 6. The base station of claim 4, wherein the message includingthe value indicating the length of time further includes information ofone or more candidate target base stations capable of accepting ahandover request.
 7. A terminal in a wireless communication system, theterminal comprising: a transceiver; and at least one processor coupledto the transceiver and configured to: transmit, to a base station viathe transceiver, a first signal for a random access, receive, from thebase station via the transceiver, a message including a value indicatinga length of time in response to transmitting the first signal, andtransmit, to the base station via the transceiver, a second signal forthe random access after a time that is determined based on the valueindicating the length of time.
 8. The terminal of claim 7, wherein thevalue indicating the length of time indicates one value identified froma plurality of candidate values, and wherein the plurality of thecandidate values has a uniform distribution between a maximum value anda minimum value.
 9. The terminal of claim 7, wherein the at least oneprocessor is further configured to determine the time based on apredetermined relationship between the value indicating the length oftime and one of a plurality of time periods, wherein the plurality oftime periods includes zero (0) millisecond (ms), and wherein the valueindicating the length of time indicates one value identified from aplurality of candidate values including
 0. 10. The terminal of claim 7,wherein the at least one processor is further configured to determinethat access of the base station by the terminal is prohibited for a timeperiod based on the value indicating the length of time.
 11. Theterminal of claim 10, wherein the at least one processor is furtherconfigured to prevent an attempt to access to the base station when thetime period has not expired.
 12. The terminal of claim 10, wherein theat least one processor is further configured to prevent an attempt toinitiate a handover to the base station when the time period has notexpired.
 13. A method performed by a terminal in a wirelesscommunication system, the method comprising: transmitting, to a basestation, a first signal for a random access; receiving, from the basestation, a message including a value indicating a length of time inresponse to transmitting the first signal; and transmitting, to the basestation, a second signal for the random access after a time that isdetermined based on the value indicating the length of time.
 14. Themethod of claim 13, wherein the value indicating the length of timeindicates one value identified from a plurality of candidate values, andwherein the plurality of the candidate values has a uniform distributionbetween a maximum value and a minimum value.
 15. The method of claim 13,further comprising: determining the time based on a predeterminedrelationship between the value indicating the length of time and one ofa plurality of time periods, wherein the plurality of time periodsincludes zero (0) millisecond (ms), and wherein the value indicating thelength of time indicates one value identified from a plurality ofcandidate values including
 0. 16. The method of claim 13, furthercomprising determining that access of the base station by the terminalis prohibited for a time period based on the value indicating the lengthof time.
 17. The method of claim 16, wherein the message including thevalue indicating the length of time further includes: an indicator forrejecting access to the base station, and an indicator for recommendinga different frequency through which the terminal is to access the basestation.
 18. The method of claim 16, wherein the message including thevalue indicating the length of time further includes information of oneor more candidate target base stations capable of accepting a handoverrequest.
 19. A method performed by a base station in a wirelesscommunication system, the method comprising: receiving, from a terminal,a first signal for a random access; transmitting, to the terminal, amessage including a value indicating a length of time in response toreceiving of the first signal; and receiving, from the terminal, asecond signal for the random access after a time that is determinedbased on the value indicating the length of time.
 20. The method ofclaim 19, wherein the value indicating the length of time indicates onevalue identified from a plurality of candidate values, and wherein theplurality of the candidate values has a uniform distribution between amaximum value and a minimum value.
 21. The method of claim 19, whereinthe time is determined based on a predetermined relationship between thevalue indicating the length of time and one of a plurality of timeperiods, wherein the plurality of time periods includes zero (0)millisecond (ms), and wherein the value indicating the length of timeindicates one value identified from a plurality of candidate valuesincluding
 0. 22. The method of claim 19, wherein the value indicatingthe length of time indicates a time period during which access of thebase station by the terminal is prohibited.
 23. The method of claim 19,wherein the message including the value indicating the length of timefurther includes: an indicator for rejecting access to the base station,and an indicator for recommending a different frequency through whichthe terminal is to access the base station.
 24. The method of claim 19,wherein the message including the value indicating the length of timefurther includes information of one or more candidate target basestations capable of accepting a handover request.
 25. The base stationof claim 1, wherein the at least one processor is further configured to:determine whether to transmit a value indicating a length of time ornot; and in case that it is determined not to transmit the valueindicating the length of time, transmit another message includingallocation information.